In processes of manufacturing a semiconductor device or a liquid display device, a plasma processing apparatus such as a plasma etching apparatus, a plasma CVD film forming apparatus or the like is used to perform plasma processing such as etching, film formation or the like on a substrate to be processed such as a semiconductor wafer, a glass substrate or the like.
Recently, as a plasma processing apparatus, an RLSA (Radial Line Slot Antenna) microwave plasma processing apparatus capable of uniformly generating a high-density plasma having a low electron temperature attracts attention (see, e.g., Japanese Patent Laid-open Publication No. 2007-109457).
In the RLSA microwave plasma processing apparatus, a planar antenna (radial line slot antenna) having a plurality of slots formed in a predetermined pattern is provided at an upper portion of a chamber. A microwave generated from a microwave generating source is radiated from the slots of the planar antenna into the chamber maintained in a vacuum state via a microwave transmitting plate made of a dielectric material and provided therebelow. A gas introduced into the chamber is turned into a plasma by an electric field of the microwave, and an object to be processed such as a semiconductor wafer or the like is processed by the plasma thus generated.
In addition, there is proposed a microwave plasma processing apparatus including a microwave plasma source in which a microwave is distributed and introduced into a chamber through a plurality of microwave introduction mechanisms having planar antennas, and then spatially compounded in the chamber (International Publication No. 2008/013112 pamphlet).
In these microwave plasma processing apparatuses, an impedance matching unit (tuner) is required to perform impedance tuning of a load (plasma). As for the impedance matching unit, there is known one using a slug tuner having a plurality of slugs (Japanese Patent Laid-open Publication No. 2003-347808 or the like).
In the slug tuner, a tube-shaped outer conductor and an inner conductor provided within the outer conductor form a coaxial microwave transmission path. Further, at least two slugs made of a dielectric material are provided in a gap between the inner surface of the outer conductor and the outer surface of the inner conductor, and movable along the longitudinal direction of the inner conductor. The impedance tuning is performed by moving the slugs by a drive mechanism. Accordingly, a compact tuner capable of reducing an amount of loss can be realized.
In this tuner, the drive mechanism for moving the slugs is provided at the outer side of the outer conductor. The drive mechanism includes a drive unit such as a motor or the like, a drive transmission unit such as a ball screw or the like, and a drive guide unit such as an LM guide or the like. Specifically, the slugs are provided with brackets which are combined to the ball screw serving as the transmission unit. The slugs are moved by rotating the ball screw by the motor and guiding brackets coupled to the ball screw by the LM guide.
When the above-described mechanism is used as a unit for driving the slug, slits through which the brackets pass need to be provided at the outer conductor, and a considerably large-sized shield mechanism is required to prevent leakage of electromagnetic waves from the slits. Further, since the drive mechanism is provided outside the outer conductor, the weight and the moment of the mechanical elements increase, which leads to requirement of a large-sized motor. Therefore, the presence of the drive mechanism limits the scaling down of the tuner.